of gums Removal waxes- review and ,, Acid + +- Lye + +- Hot water Heuer Processing

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1 ,,. Processing Removal of gums and waxes- A review This article is by veronique Gibon and Alain Tirtiaux, of Practionnement Tirtiaux, Pieurus, Belgium. Holdingank Centrlfugal separator - Acid lye - Hot water Heuer Centrlfugal separator, Fllure I. Americ (Ionl-mlx) method The refining of edible oils and fats can be operated according to rwo main routes: chemical refining and physical refining, each consisting of a series of operations conducted to remove mainly gums, metals, pigments, hydroperoxides, waxes, and free fatty acids. The principal difference berween chemical and physical refining is how the free fatty acids are removed. Degumming methods Chemical refining. In a chemical operation, the oil is cleared of gums and free Iarry adds during the neutralization step. The "long-mix" technique (Figure 1) was developed based on a long-rime/lew-temperature sequence especially designed to treat fresh North American soybean oil. Refining cottonseed oil in the miscella State is also based 00 this type of sequence. The "short-mix" rechnique consists of a short contact time at higher temperature (Figure 2). With this technique, conditioning of gums with phosphoric acid takes care of higher levels of nonhydratable pbospharides, fixed gossypol from cotronseed oil is more easily removed. RE-REFINING(optional) - Acid Crude 011 Holding tank - Lye { - Hot water (or lye) - Hot water ] Refiningor drying for stonlge Fllur. 2. Standard (short-mix) f'leutrajiu.tion Volume II May 2000 Inform

2 S25 In a chemical refining, the heavy phase is a soapstcck, which normally requires further treatment. Physical re(illil/g. If the physical refining option is chosen, most free ferry acids are carried through to (1 deodorizing unit. Operating ccndi- (ions (temperature, vacuum, and steam) are carefully controlled in order to allow the distillation and steam stripping of the acids. A welldesigned deodorizer operating at an acceptable efficiency will reduce the COStS of the process. As distillation requires a higher-temperature treatment, the oil must be carefully degummed and bleached before entering the deodorizing unit. Water degumming (Figure 3) is the simplest method for phosphatide reducrion; however, only the hydratable phosphatides can be removed by mixing the oil with only water. This means that typical gum contents after water degumming can still lie between 80 and 200 parts per million (ppm) of phosphorus, depending upon the type and the qualiry of the crude oil. With its Alcon process, the Lurgi organization proposes a seed preparation before solvent extraction; a crude oil with a very low content of nonhydratable phosphatides results; as a consequence, Alcon-processed oil can be degummed by water to residual phosphorus levels of ppm. Hot water MIXer Refining or drying (or stor.lge Heuer Acid Hct water Holding unk Centrifugal separ.ltol" Refining or drying for stor.lge a Figun! 4. (a) Simple acid degummlnc; As the nonhydratable phosphntides also have to be removed, they must be activated by different methods. At the present time, the preferred procedure is add degumming [simple acid degumming, ultrafiltration (UF) degumming, special degumming, IMPAC (improved acid) degumming, super/unidcgumming, top degumming], where the gums are conditioned into a hydra table form leading to oil-insoluble metal salts and to phosphatides in their acidic state. Oils with a low phosphatides conrent, such as palm oil, palm kernel oil, coconut oil and animal fats, can be degummed using the simple acid degumming technique (Figure 4). The hot crude oil (80-90"C) is thoroughly mixed with phosphoric or citric acid, followed by a reaction time of approximately 5-20 minutes; 2-5% of water is thoroughly mixed with the oil before it is routed to a cenrrifuge separarcr, These oils can also be treated according to- a dry degumming sequence. In this case, the phospharides are simply addtreated and absorbed directly in the bleaching unit. Krupp has developed Acid Holding unk Bleaching b (b) dry dejumminc which a conventional simple acid degumming will not achieve a level of 3-5 pprn of phosphorus as required for final steam-stripping refining. The oil is heated and mixed with acid for conditioning the gummy substances; after cooling, a flocculating agent and, if necessary, soft water are dosed into the oil before it is moved into a retention tank where the gums are coagulated. After this, the oil is heated and centrifuged, and eventually washed and Acid Aocculating agent water Centrifugal separ.ltor Refining or drying for stor.r.ge the UF degum- Ficun! l. Water decummlna ming (Figure 5) for vegetable oils for FII'ln! 5. Ultrafiltration (UF) decumming Volume I I May 2000 Inform

3 Acid (Speci..! ilddltive)... Lye: Hot water Holding tank Centrifugalsen.tor... - Hot water RefinIng or drying for storage Figure 6. Special degumming (Alfa-Lanl) Processing Crude on... - lecithin... - Acid Holding lank Cooler... - War Hydration tank CenDifugal 5epanltOr COO" l)'1i! Holding and agglomeration a.nk Centrifugal separator Refining or drying for storage Figure 7. Superlunidegumming (Un1iever)... - Acid... - l)'1i! Centrif'upl separator... - War Refining or drying for storage Firure 8. Top derummlng (Vandemoortele) centrifuged again, before entering the bleaching unit. Alfa-Laval's special degumming process (Figure 6), also called acid refining, has been developed for highphosphatide content oils, such as soybean, sunflower, and rapeseed. The crude oil is heated at 70 C and the gums are treated with phosphoric or citric acid by mixing, followed by a retention time of approximately five minutes. A critical quantity of dilute caustic soda is added to neutralize the acid. If the degree of neutralization is roc low, then the viscosity of the gums is too high, leading to difficulties in the centrifugal separator; if it is too high, portions of the free fatty acids are transformed into soaps, leading to higher losses due to emulsification. Water is then added to the neutralized mixture, with 20 minutes required for the total hydration of the gums, before a second centrifugation. In case of high-quality oilseeds, acid, diluted caustic soda, and water can be mixed with the oil before the first centrifugal separator, thereby saving investment COSts. In De Srner's IMPAC degumming, special additives are simply added before the citric acid and caustic soda in order to improve the wetting of the nonhvdraeablc phcspharides and hence their solubility in the aqueous phase. Unilever's superdegumming (Figure 7) is based on the fact that hydra table phospherides containing polar groups can form liquid crystals when they are put in contact with water at low temperature. The crude oil (sometimes treated with lecithin) is heated (75 q, thoroughly mixed with citric acid, and sent into a 15-minute retention tank. The whole is then cooled to 25 C and held for three hours after addition of warer, during which the phosphatides develop their crystalline form. After heating, the gums are separated in a centrifugal separator. At this stage, the phosphorus content is only ppm, so the oil must undergo a second step before physical refining. The superdegummed oil is first cooled to 40 C, treated with a small quantity of dilute caustic soda, held for two hours, heated, and finally centrifuged. At the end of this combined super/unidegumming, the phosphorus content has fallen below 5 ppm, and the wax content is lowered. Vandemoortele, with some assistance from Westfalia, has patented a process called top degumming (Figure 8). The crude oil is heated at "C and intensively mixed with phosphoric acid; after a retention time of approximately three minutes, the phosphoric acid is partially neutralized with dilute caustic soda and the components are separated in a cenn-ifuge. In a second stage, hoc water is added and after a short residence time, the separation takes place Volume I I May 2000 Inform

4 Citric acid.. e-, NaOH Agitated holding tank..... Enzyme ReactOr Refining or drying for storage Figure 9. Enzymu: procels (Lurgl).. - Chemicals water Refining or drying for storage a b., P < Sppm Fe <O.lppm Figure 10. (a) S.O.F.T. degumming (Tirtlaux); (b) flowsheet (or a S.O.F.T. degumming plant on a special high g-force centrifugal sep araror, Phosphorus levels lower than 5 ppm characterize top-degumrned oil. Besides acid degumming, Lurgi's Enzymax process (Figure 9) consists in mixing the oil with citric acid and caustic soda to a buffered ph 5 into which phospholipase is dispersed. The enzyme is given sufficient lime to catalyze the conversion of non hydra table pbosphatides into oil-soluble lysophosphatides, which are then removed by centrifugation, yielding a degummed oil low in phosphorus. In the S.O.F.T. degumming (Figure 10) system patented by Tirtiaux, the oil is heated (7S-8S"C) and mixed with a water solution (2-5%) containing a wetting agent and a cornplexing molecule that is able to form a Strong chelate with a series of ions, including magnesium, calcium, and iron. The divalent component of the water-insoluble, nonhydratable phosphatides can be removed through the chelating action of EDTA (ethylenediaminetetraacetic acid). Subsequent hydration of the phospharides for a period of 20 minutes and centrifugation provide a degummed oil with a phosphatide conrenr lower than 5 ppm. The efficient removal «0.1 ppm) of iron as an oil-insoluble complex with EDTA confers to the degummed oils an improved oxidative stability and lowered risk of deterioration of the refined oils. The main advantage of this process is its simplicity as it only needs a special mixer (high-shear) and one centrifugal separator (selfcleaning). Phosphorus contents lower than 5 ppm can be anticipated for any crude or water degummed oil contain-... Ia. -" ""' pow In 0M0i0n ct"'lliet. To join, contact: AOCS, Membership, P.O. Boll 3489, CIwnpaign, IL USA. I'ttone: ; fax: ' _8091; membershipthlocs.org. Volume I I May 2000 Inform

5 Processing 528 Table I Characteristics of different crude and water deaummed oils, S.O.F.T. degummed In pilot plant (phosphorus by AOCS Ca 11-55; calcium, magnesium, and Iron by ICP lpectrometry) Oil PV FFA Phosphorus Calcium Magnium Iron '%1 (ppm) (ppm) (ppm) (ppm) Water- Before degurnmed After soybean Water- Before degummed After 2.' soybean " " " 35 I.' Water- Before L5 II L5 degummed After rapeseed Crude Before sunflower After I.' " 0.04 Crud, Before 0.' m II. 3.2 soybean After " 0.05 Crude Before 0.' I.' rapeseed After O.oJ I.' Crude corn Before After Crude palm Before 2.5 8, 3 4 After Crude palm Before '.3 After 2.' ing high or low levels of phospheridcs (Tables I and 2). The simplicity of the system makes it possible for the refiner ro switch from alkali refining or from any other degumming process ro the present one at very low COStS. Nore that although membrane techniques for degumming oils have been tested successfully 3S laboratory and pilot-plant scales, they have not been applied yet on a large industrial scale. Wax content and cold stability, an update The quanritarive measurement of waxes in oil can be done by chromatographic techniques, but it is rime-consuming and for this reason many companies have chosen to use the rurbidimerer (correctly calibrated) as a rapid and adequate method for wax content measurements. In cases when such equipment is nor available, the cold test is normally used as reference: a dewaxed sunflower or corn oil remaining clear for at least 24 hours at ooe corresponds roughly to a wax content below 50 ppm. Nevertheless, it has been noted that despite passing a 24-hour cold test, an oil may develop a haze after a few days of storage at room temperature in a clear bottle. This is probably due to a viscosity problem at aoc that delays the crystallization of the waxes. For this reason, some users prefer [0 perform the cold test of dewaxed sunflower at Ire. The cold-test stability also depends upon local requirements; for example, in cold countries, a 48-hour cold test at ooe is usually required, corresponding to a wax content of roughly 15 ppm. Dewaxing VS.winterization "Dewaxing" and "winterization" are often confused. "Dewaxing" consists in removing waxes from the oil by using one of the above-mentioned techniques. "Winterization" is a term commonly used ro describe the removal of any solid particles rhat can cause cloudiness of the oil during storage. Such particles can be waxes, polymerized oil, and even saturated triglycerides. If sarurared triglycerides are to be removed, [he term "frac- Volume I I May 2000 Inform

6 '" Table 2 W;ateMieaummed 5O)'bean 011, crude com, sunnower and palm oils, S.O.F.T. degummed In Industrial pl;ants (4 Tlhour) (phosphorus by AOCS Ca 12 55; calcium, magnesium,;and Iron by ICP $pectrometry). Oil Phosphorus (ppm) Before treatment Phosphorus (ppm) After treatmem Water degummed (FFA: %) soybean ' 5-' Crude com (FFA: %) ' ' ' ' Oil FFA Phosphorus Calcium Magnesium Iron (%1 (ppm) (ppm) (ppm) (ppm) Crude Before I.S ' I., sunflower Afler ",0.1 Crude palm Before After rionarion" is more appropriate. At rimes the full dewaxing process is divided into two parts: dcwaxing, which allows reduction of the wax conreur to approximately ppm (for example by combined neurralization/dewaxing or by superlunidegumming), and winterization, which involves a polishing filtration of a dewaxed oil. According to this, one could say that it is nor necessary to winterize a S.O.F.T. degummedj dewaxed oil. zarion, refers rc the removal of highmelting-point waxes that are responsible for the turbidity of the oils when exposed to storage conditions in the supermarket or in the refrigerator. Waxes are long-chain fatry acid esters of long-chain fany alcohols, which to some extent crystallize under room temperature and certainly at refrigerator remperarure, leading to the clouding of the oil. As 3 result, the appearance of the oil in transparent bonles is altered, which reduces the marketability of the product. In a typical conventional dewaxing merhod (Figure I l}, the neutralized oil is cooled under constant agitation to a temperature of approximately 4 C, A seeding material that also can act as filter aid in the filtration operation (Kieselguhr, Perlite, or wood pulp) is often added to improve the crystallization of the waxes. The oil is transferred to a maruraror; under weak agitation. Dewaxing Several oils, mainly sunt1ower, corn, safflower, rice bran, grapeseed and olivepomace oils, contain waxes that must be removed during the refining process. Dewaxing, which is a form of winreri- Filler aid Neutralized oil... I Cooler I Crystallizer I... I Filter I - Dewaxed 011 FI,ure I I. Conventional dewu.ina Volume I I May 2000 Inform

7 Processing 5lO Diluted caustic soda Oilout of first centrifuge... I Huter I... I 1.. I Cooler I Cold water... ICrystalHzers I - IHuter I.. I I.. I I Hot water I I - ICentrifugal sepmrorl - Neutrarll:edidewued oil Flaul"e 11. [)ewaxinlu an extension of the neutnllz.ation step When the growth of the wax crystals is completed (4-16 hours), the oil is transferred to the filtration unit (after mild heating at a maximum temperarure of 15 C) where the separation takes place on pressure-leaf filters. This method is still widely used for oils with a wax content of less than 500 ppm, which is more or less an upper limit, as filtration problems can occur at greater wax contents. Another dewaxing system that has been proven effective is to use simple rapid cooling and filtration of the oil without using any marurator. The dewaxing of high-wax content oils is generally integrated as an extension of the neutralization step (Figure 12) of chemical refining (Figure 2). The oil is heated to C, and a small quantity of acid is added; the retention time is approximately three [Q five minutes without agitation. High-temperature caustic soda is dosed [Q neutralize the free fatty acids (and the acid itself); a rerenrion time of five minutes is required before centrifugation. Downstream of this step, diluted caustic soda is dosed to reach a higher level of soaps (at least 2,500 ppm), which are used as agglomerating agents of the waxes. The whole is then cooled to approximately 5 C before entering a series of crysrallizers. At the end of this, cold water is added and then removed with the crystallized waxes and soaps in a second centrifugation, after heating at 15"C to reduce the viscosity. Final washing is performed either at C or at low Acid - Caustic soda -e I I... I Crystallizer I.. I Hot water.. ICentrifuel separator!.. I I _ I I - I I - I Cooler I _ [ Centrifuplseparatorl.. Neutn.liudldewaxed oil FiJUI"e Il. Cold nlftnln, Volume 11 May 2000 Inform

8 531 Neuu.lized. or bleached or decdortzed oil... I Cooler I Filter aid I Crystallizer I... Filter... Dewaxed 011 Flaure 14. Polishing filtration temperature before the oil goes [Q the bleaching section. Depending upon the cold test requirements, a polishing filtration can be recommended. Cold refining (Figure 13) is an alternative for oils with low acidity; otherwise, the oil losses would be too high. After dosing with a small quantity of acid for a short time, the oil is cooled. Caustic soda is then added to neutralize the free fatty acids, and the whole is sent to crysrallizers, to allow wax crystals to grow. After several hours, the mass is centrifuged, and the dewaxed oil is washed at high temperature and centrifuged again. Polishing filtration (Figure 14) is generally carried out before or after bleaching and, less frequently, after deodorizing. In the latter case, the oil is cooled to 12-1S"C and kept hours without agitation. Filtration is done after the addition of filter aid. Even if this procedure is economically interesting (because the oil, in any case, has to be cooled at the coder of the deodorizer for storage), some problems of increases in peroxide or of polymerization products during the deodorizing of any nondewaxed oil can be encountered. Polishing filtration between the bleaching and deodorizing steps is not economical from an energy point of view. The main interest lies, however, in the use of dried oil, which prevents any problems during filtration, and in the fact that oil entering the deodorizing unit is free from waxes. To polish before bleaching would be economically ideal, at the point where the remaining wax crystals are still in the oil as solids, that is, after the second centrifugation (or the third one if washing is performed). The only problem lies in the % moisture in the oil, requiring special attention during the filtration. When a choice has to be made berween physical and chemical refining for the treatment of oils with high wax contents, the question of the efficiency of the dewaxing is often brought up for consideration. Up to now, a slightly modified super/unidegumming was the only possible way (0 reduce the wax content while degumming. During the hydration of the phosphatides at low temperature (25 q (Figure 7), pan of the waxes also crystallize and can be removed together with the gums. If this temperature is lowered to SoC. partial winterization can be achieved. Polishing filtration is nevertheless necessary to reach strict cold-stability requirements. The lack of any easy solution to degumming and dewaxing of oils with a high wax content has pushed development of a new concept that is mainly based on a modification of the S.O.ET. degumming, giving rise to the S.O.ET. degumming! dewaxing process (Figure 15). 5m P < 5ppm Fe < O.lppm Flsure 15. Flow sheet of 5.0. F.T..JUmmina/dewaxlnl plant Volume I I M;ay 2000 Inform

9 Processing SJ2 Table 1 Char.u:terlstlu of S.O.F,T.degummedldewued com and sunflower oils In pilot plant (pholphorus by AOeS Ca 12 55;a.lcium, magne. sium,and Iron by ICP lpe«rometry) Oil PV FFA P C. M. F. Cold (%) (ppm) (ppm) (ppm) (ppm) Test (h) O C ra-e.' Room temp. C ) 11.7 U A' " 0.1 >.,. >72 >5,"" c a <0.' I.. A ' >.,. >72 >5,"" A >.,. >72 >5,"",",- e , e 32 I.' Sl ' A >.. >72 '"""- " >5 '"" > l.5 1<4.6 0.' A U " 0.03 >.,. >72 >S days Sunflower e 0.92 < I.l A U 0.1 O.OS 0.05 >.,. >72 >5,"" Sunflower e ' I.' A I " O.OS >." >72 >5,"" SunflO'M!r e '.3 A U >.. >72 >5,"" Sunflower a , A 2.' >.. >72 >$ days Q Before treatment: b Afttr treatment After [he oil is heated (75-SSoq and mixed with the water solution containing the wetting agent and EDTA, [he emulsion is cooled to 6-S"C and senr to a weakly agitated marurutor (8-10 hours), where growth of the wax crystals occurs. The oil is then heated at ls"c to reduce the viscosity before the subsequent separation in a centrifugal separator. As small amounts of soaps are produced during the degumming process, washing is not necessary, which Volume I I Ma2000. Inform permits a saving in equipment. Oillosses during the centrifugation at low temperature are very low. During the degumming, the hydrated phosphatides are preferentially located at the oivwater interface. The growth of the waxes therefore takes place in the midst of a degummed oil. It is indeed well known that phospharides strongly delay or inhibit the crystallization of the waxes. Crystallization in a medium where phosphaeides are already "trapped" at the oil/water interface is therefore improved. As a consequence, the degummed/dewaxed, bleached and deodorized/deacidified oil has a cold test of 48 hours minimum at O C, and further polishing filtration is not necessary. Finally, as the combined degummingldewaxing occurs before bleaching and deodorizing, the risk of peroxide formation as found in conventional methods of deodorization followed by dewaxing is reduced.

10 SJ3 60 c = 30 E d d 20 c y '" x R2 '" Ions (ppm) -ICP Figure 16. Correlation between titration..nd sp<ectj'ometic method (ICP) for th" determl. nation of Ion content (calcium, mnesium.;and iron) of oils Physicit.lly refined sunflower and corn oils The combined S.O.F.T. degumming! dewnxing technique was first developed all a pilot scale with different qualities of sunflower and corn oils. The oil is heared at C, thoroughly mixed with a water solution containing wetting agent and EDTA, cooled co 6"C, and held for eight hours in a maruraror, Afrer heating at ISoC, the oil is separated by centrifugation from the water solution containing gums and waxes. Such dcgummedldewaxed oils are characterized by low levels of phosphorus (P < 5 ppm), as well as cold-stability characteristics of completely dewaxed oils (Table 3). Moreover, in every case, the iron content is extremely low, giving the degummedldewaxed oil very good oxidative stability. It is obvious that the analysis of phosphorus is not representative of the quality of the oil in terms of nonhydratable phospharides. As the lack of hydrarabihry of the phosphatides is mainly due to their complexation with calcium, magnesium, and iron, the quantity of these cations can be directly linked to the content in nonhydrarable phosphatides. This information is important to optimize the process in terms of reagent consumption. For this reason, a rapid and reliable method for determining the content of inorganic ions in the oil has been developed. This method, based on extraction followed by cicraricn, has been successfully correlated to the spectroscopic results obtained from ion core plasma inductively coupled plasma (ICP) spectrometry (Figure 16). This degummingldewaxing process has been developed in a refinery running at a capacity of four rnerric rons per hour for sunflower and corn oils. The shortmix process has been slightly modified in a S.O.ET. degurruningfdewaxing plant. A high-shear mixer was installed to mix oil and water, and the water-in-oil emulsion sent to one existing crystallizer; after eight hours at 6 C, the mixture was pumped, after heating at 15 D C, to the centrifugal separator; where the oil was sampled. The analysis of the continuous process for a specific batch of sunflower oil is presented in Table 4. The degummedldewaxed oil described was then bleached and deodorized/deacidified in a physical refining process. The characteristics of the fully refined oil are described in Table 5. Table.. Characteristics of sunflower oil, before &nd after S.O.F.T. degurnrnlngidewaxinj In an industrial plant at -4 Tlhour Acidity (%) Peroxide value (meq!kg) Totox Phosphorus (ppm) Ions (ppm) Waxes (ppm) Soap (ppm) Cold rest (hours): we 12"<: Room temperature Q By ICP spectrometry Sunflower oil ' D 800 S.O.F.T. degummedj dewaxed oil 1.1 <1 20 >48 >72..5 days Volume I I May 2000 Infarm

11 ". Processing TaiMe 5 Characteristics or. refined lu""_r oil, with S.O.F.T.decummin&!dewaxln,u preueaanent in UI industrial plant at. metric toni per hour feed oil S.O.F.T. d""""",,,,, dewaxed (SDD) SOD bleached (SODB) SDDB deodorized (fully refined) AcidiTY ('Yo) <0.05 Phosphorus (ppm) Calcium 18.4 (ppm)" Magnesium (ppm)" S., Iron (ppm)" I., <0.1 PV (meqlkg) 3.7 Lovibcnd IRl30Y (1") 4.3 R/40Y (5"114) 0.7RJIOY l5' 1/4) O.4RJ ts- 1/4) Waxes (ppm) 800 Cold tor (hours) >48 at O"C >72 at 12"C > 5 days at room temp. a By ICP spectrormuy. As the process is performed under acidic conditions (ph 5), there is no saponification of the feed oil; the slight reduction of the oil acidity is only due to a side reaction of the unbalanced [EDTA-CaIMg] complex with the free fatty acids. EDTA can be found as its full acidic form (H4EDTA) or in a dissociate form (HEDTA-. H2EDTA--. HEDTA3-, EDTA -J depending upon the ph conditions. The doubled dissociated form H2EDTA-- is stable in moderate acidic media (ph 3-6), giving rise to the following reaction: H2EDTA- 2 Na phosphatide-ca IMg-- [EDTA-CaIMg l" 2 Na" 2H phosphatide The unbalanced IEDTA- CaIMgj-- complex probably removes any free fatty acids as insoluble soaps. A conventional dewaxing process accompanied by the neutralizing step used in a caustic refining plant gives rise to several problems: The addition of dilute caustic soda after the first centrifugation increases the soap content to 2,500 ppm, with a risk of neutral oil losses by saponification of the t riglycerides. The high soap content has a negative effect on the neutral oil losses during the separation at low temperature. A final washing at high temperature is performed because the soap content in the oil after the second centrifuge is still above 600 ppm; three centrifugal Volume I I May 2000 Inform

12 Sl5 separators are therefore necessary in such dewaxing plants. A polishing filtration is necessary to achieve strict cold-stability requirements. In the S.O.F.T. degummingldewaxing, there is no risk of saponification of the neutral oil, the soap content in the oil is very low, and only one centrifugal separator is necessary. In the model of water-in-oil emulsion, the growth of the waxes takes place in an already degummed oil. As a consequence, this mechanism is greatly improved, and good cold rests are achieved without requiring any polishing filtration. High and low levels of waxes can be easily removed before bleaching or drying if the oil has to be stored. Conclusions Up to now, the physical refining of waxcontaining oils, such as sunflower oil or com oil, was possible by the conventional method, using pressure leaf filters for the separation of the low-temperature crystalliz.ed waxes. This method can, however, be problematic when there is a high wax content. The superlunidegumming with the hydration step performed at low temperature is another possibility, but in this case, polishing filtration is still required depending upon the cold-rest stability requirements. The main interest in the combined degummingldewaxing is its simplicity, as only one high-shear mixer, low-ternperature residence tanks, and a selfcleaning centrifugal separator (as well as heat-exchangers) are necessary to achieve very strict cold stability requirements. Compared with dewaxing accompanied by the neutralization step of caustic refining, the neutral oil losses due to soap formation are low with the new procedure. For all those reasons, (he combined degummingldewaxing used in the pretreatment of physically refined oils appears to be a very promising approach. Bibliography Bailey's Industrial Oil and Fat Products (Fifth Edition), Volume 2, edited by Y.H. Hui, John Wiley & Sons Inc., New York, New York, Degumming and Neutraliuztion of Fats and Oils, Alfa-Laval Separator AB, Industrial Separation Division, Tumba, Sweden, Processing Lines for the Edible Oil Industry, GEA Mechanical Separation Division, Westfalia Separator AG, Oelde, Germany, Update on Filtration in the Processing Steps of Edible Vegetable Oils, LF.C. Lochem B.V., Lochem, The Netherlands, UF Degumming, Krupp Maschinen-rechnik GmbH, Hamburg, Germany, Dijkstra, A.J.. Degumming, Refining, Washing, and Drying Fats and Oils, in Proceedings of the World Conference on Oilseed Tech"ology and Utilization, edited by T.H. Applewhite, AOeS Press, Champaign, illinois, 1992, pp Buchold, H., Enzymax, a State of the Art Degumming Process and Its Applications in the Oil Industry, Lurgi 01 - Gas - Chemie GmbH, Frankfurt am Main, Germany, Deffense, E., S.O.F.T. Degumming, in Oils-Fats-Lipids, Proceedings of the 21st World Congress of the International Society for Fat Research (Volume 1), P.]. Barnes & Associates, Bridgwater, England, 1996, pp Gibon, V., and A. Tirtiaux, S.O.F.T. degumming: The simple route to physical refining of soft oils, Malaysian Oil Sci. Technoi. 7(2),48-54 (1998). Gibon, V., and A. Tirriaux, EI proceso de desgomado S.O.F.T., Aceites Graws 32: (1998). Gibon, v., and A. Tirtiaux, Un Raffinage S.O.F.T., Oliaginellx Corps Gras Lipides 5: (1998). S.O.F.T. degumming, a process for the mill, in Proceedings of the 1999 PIPOC Conference, Emerging Tedmofogies and Opportunities in the Next Milfem,;um-Chem;stry and Tec.hnology, Palm Oil Research Institute of Malaysia, Kuala Lumpur, Malaysia, Determinacion of ion content in oil, Procedure SDOO1 (internal documentation), Fractionnement Tirtiaux, FJeurus, Belgium, 1998.D Volume I I MOly Inform